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921.
922.
The glass transition behavior of a La55Al25Ni20 amorphous alloy was examined through the changes in the storage, E′, and loss, E″, moduli obtained by a forced oscillation method. Two distinguishable relaxation peaks are observed in the glass transition region, although these are not resolved in calorimetric measurements. At a frequency of 62.8 rad/s, E″ shows two peaks at 483 and 507 K. As the frequency decreases, the splitting of the two peaks becomes distinct and their peak temperatures shift to a lower value. The change in E″ with frequency also shows the two relaxation peaks. A master curve of E″ is derived by using the time-temperature superposition process. This is the first master curve for the relaxation spectrum in the glass transition region for amorphous alloys. The activation energies evaluated from the shift factors are 400 and 550 kJ/mol for the lower and higher temperature peaks, respectively. 相似文献
923.
Hideyasu Ando Toshio Fujii Adarsh Sandhu Tsuyoshi Takahashi Hideaki Ishikawa Naoya Okamoto Naoki Yokoyama 《Journal of Crystal Growth》1992,120(1-4):228-233
High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI2H6 (n = 9 × 1017 cm-3), and the base layer (92.5 nm) was doped with carbon from TMG (p = 4 × 1019 cm-3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 104 A/cm2. The device characteristics of our carbon-doped HBTs were found to be stable under current stress. 相似文献
924.
925.
926.
Yusuke Fuji Kazuya Watanabe Kyung‐Youl Baek Tsuyoshi Ando Masami Kamigaito Mitsuo Sawamoto 《Journal of polymer science. Part A, Polymer chemistry》2002,40(12):2055-2065
A hydrophilic ruthenium complex with ionic phosphine ligands { 1 : RuCl2[P(3‐C6H4SO3Na)(C6H5)2]2} induced controlled radical polymerization of 2‐hydroxyethyl methacrylate (HEMA) in methanol under homogeneous conditions; the initiator was a chloride (R‐Cl) such as CHCl2COPh. The number‐average molecular weights of poly(HEMA) increased in direct proportion to monomer conversion, and the molecular weight distributions were relatively narrow (Mw/Mn = 1.4–1.7). A similar living radical polymerization was possible with (MMA)2‐Cl [(CH3)2C(CO2CH3)CH2C(CH3)(CO2CH3)Cl] as an initiator coupled with amine additives such as n‐Bu3N. In a similar homogeneous system in methanol, methyl methacrylate (MMA) could also be polymerized in living fashion with the R‐Cl/ 1 initiating system. Especially for such hydrophobic polymers, the water‐soluble ruthenium catalyst was readily removed from the polymers by simple washing with an aqueous dilute acid. This system can be applied to the direct synthesis of amphiphilic random and block copolymers of HEMA and MMA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2055–2065, 2002 相似文献
927.
Ammonia synthesis by means of plasma over MgO catalyst 总被引:1,自引:0,他引:1
Kazuo Sugiyama Kiyoshi Akazawa Masaaki Oshima Hiroshi Miura Tsuneo Matsuda Okio Nomura 《Plasma Chemistry and Plasma Processing》1986,6(2):179-193
Ammonia synthesis from H2-N2 mixed gas was studied at room temperature in a glow-discharge plasma in the presence of metals or metal oxides. Magnesia (MgO) and calcia (CaO), which are oxides with solid basicity, revealed catalytic activity in the plasma synthesis of ammonia, although they are catalytically inactive in industrial ammonia synthesis. The acidic oxides (Al2O3, WO3, and SiO2-Al2O3) lead to the consumption of the reactant, i.e., the H2-N2 mixed gas. No ammonia was isolated. Metal catalysts showed higher activity than the above basic oxides. They have, however, different activities. The reaction was faster over the active materials than over sodium chloride (NaCl) or glass wool or in a blank reactor without any catalyst. 相似文献
928.
929.
930.
Synthetic Control of the Excited‐State Dynamics and Circularly Polarized Luminescence of Fluorescent “Push–Pull” Tetrathia[9]helicenes
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Yuki Yamamoto Dr. Hayato Sakai Dr. Junpei Yuasa Prof. Yasuyuki Araki Prof. Takehiko Wada Prof. Tomo Sakanoue Prof. Taishi Takenobu Prof. Tsuyoshi Kawai Prof. Taku Hasobe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):4263-4273
A series of fluorescent “push‐pull” tetrathia[9]helicenes based on quinoxaline (acceptor) fused with tetrathia[9]helicene (donor) derivatives was synthesized for control of the excited‐state dynamics and circularly polarized luminescence (CPL) properties. In this work, introduction of a quinoxaline onto the tetrathia[9]helicene skeleton induced the “push–pull” character, which was enhanced by further introduction of an electron‐releasing Me2N group or an electron‐withdrawing NC group onto the quinoxaline unit (denoted as Me2N‐QTTH and NC‐QTTH, respectively). These trends were successfully discussed in terms of by electrochemical measurements and density functional theory (DFT) calculations. As a consequence, significant enhancements in the fluorescence quantum yields (ΦFL) were achieved. In particular, the maximum ΦFL of Me2N‐QTTH was 0.43 in benzene (NC‐QTTH: ΦFL=0.30), which is more than 20 times larger than that of a pristine tetrathia[9]helicene (denoted as TTH; ΦFL=0.02). These enhancements were also explained by kinetic discussion of the excited‐state dynamics such as fluorescence and intersystem crossing (ISC) pathways. Such significant enhancements of the ΦFL values thus enabled us to show the excellent CPL properties. The value of anisotropy factor gCPL (normalized difference in emission of right‐handed and left‐handed circularly polarized light) was estimated to be 3.0×10?3 for NC‐QTTH. 相似文献